1. Field of the Invention
The invention relates to a welding device and a welding method and, more particularly, to a welding device and a welding method for welding with the use of electrodes.
2. Description of Related Art
For example, spot welding is carried out as a method of joining two or more steel sheets. Sport welding is carried out as follows. First, two or more stacked steel sheets are sandwiched at a high pressing force (for example, about several thousands of newtons) with the use of, for example, two copper electrodes (welding tips), and a current (for example, several thousands to several tens of thousands of amperes) is flowed, between the electrodes. After that, resistance heat arises due to the current flowing through the steel sheets, and the stacked steel sheets are welded together as the steel sheets are melted by the resistance heat.
When a worker has erroneously sandwiched an object other than a welding target, such as a worker's finger, between the two electrodes at the time of welding, a method of detecting the fact that the object other than the welding target has been caught in is introduced. For example, there is a method of detecting the fact that an object other than a welding target has been caught in on the basis of the position of the electrodes. Specifically, it is a, method in which it is determined that it is abnormal when a displacement by which a movable electrode has moved until the movable electrode contacts the welding target is small and then the electrodes are released.
Japanese Patent Application Publication No. 61-283469 (JP 61-283469 A) describes a lower electrode consumption state determination device of a stationary spot welding machine, which includes a current detector for detecting a welding current flowing through a lower fixed electrode and a determination circuit that measures a welding current value and an energization time on the basis of an output of the current detector and informs that welding is inappropriate when any one of the welding current value and the energization time is smaller than a corresponding one of comparison reference values by comparing both measured values with the corresponding reference values.
When spot welding is repeatedly carried out, the distal ends of the electrodes abrade. Thus, as described above, with the method of detecting the fact that an object other than the welding target has been caught in on the basis of the displacement of the movable electrode, that is, the position of the movable electrode, for example, it may not be able to correctly determine whether an object other than the welding target has been caught in when the electrodes have abraded.